August 7, 2013

Dolphins Can Store Memories For Up To 20 Years

It's been previously discovered that dolphins are capable of recognizing the voices of their peers and even mimicking these sounds from their closest friends.

Now, researchers from the University of Chicago say dolphins are capable of remembering these calls for 20 years or more, making them the animal with the best memory. This also places their level of cognition highest amongst chimps, elephants and humans.

According to Jason Bruck, the study's head author from the University of Chicago, this embedded memory of sound could even last longer than a human's facial recognition memory. The study is now published in the latest issue of the Proceedings of the Royal Society of London B.

"This shows us an animal operating cognitively at a level thatâ€™s very consistent with human social memory," explains Bruck who received his PhD in June in Comparative Human Development. He and his team, studied 53 bottlenose dolphins at six different locations, including a Zoo in Chicago and a Dolphin Quest aquarium in Bermuda. Each of these locations have been rotating which dolphins they keep in their aquariums and, most importantly for Bruck, keeping good records on which dolphins once lived together in the same tank.

Knowing this, Bruck and team first recorded the calls of each of the bottle nose dolphins, then began to play sounds of random dolphins not in the study via underwater speakers. Bruck says the animals got bored of these foreign calls pretty quickly and eventually began to ignore them altogether. Next he played them signature whistles of other dolphins they may have previously lived with.

"When they hear a dolphin they know, they often quickly approach the speaker playing the recording," said Bruck in an interview with the AFP. "At times they will hover around, whistle at it, try to get it to whistle back."

To test their memory, Bruck and crew began reaching deep into the catalogue to find the calls of dolphins they lived with many years ago. To their surprise, these animals not only remembered, they remembered tank mates from many years back.

"I was expecting five, maybe 10 years. Memory for over 20 years just has not been systematically shown in animals so I was amazed by what I found," said Bruck. Twenty years also happens to be the average life expectancy for dolphins living in the wild, though they can live to be as old as 45.

In an interview with National Geographic, Bruck says some of the dolphins enjoyed hearing their old friends so much, they'd get as close to the speaker as they could -- so close, in fact, that they'd block the noise entirely. Others would begin speaking directly to him as if to ask how their old friends have been doing. Bruck also mentions a particular group of dolphins that began mimicking the calls of other dominant males during the experiment, in order of rank, almost as if they were requesting to hear their voices instead.

According to Bruck, it may be important to remember the voices of other dolphins to help them recognize lost family members or even avoid rival dolphins.

"Having a long term social recognition for that ecological reason can be the difference between an animal having a very negative social interaction and a positive one," said Bruck.